Brainworms and ticks are decimating an animal sacred to the region’s original inhabitants.

April McCormick was a teenager when she killed her first moose. A chill cut through the forest on a late-October morning as she tried quieting her footfalls, like her step-dad taught her, and eyed the surrounding tree trunks. Were the lower branches stripped of leaves? Was the breeze carrying a whiff of scat?

A rumble rose behind her. She turned around and saw it — an enormous bull moose, its antlers brushing a nearby birch. She raised her rifle. “I took a few deep breaths,” McCormick, now in her 30s, recalled in an interview with Vox, “and took the shot.”

Formative experiences involving moose were once commonplace in northeast Minnesota on the north shores of Lake Superior, home of the Ojibwe people. That includes McCormick and her family, who have lived in the region for centuries. Indigenous communities in the US and Canada consider the animal a “cultural keystone,” historically both a critical food source and an integral part of spiritual and cultural practices.

A single moose can yield upward of 700 pounds of meat, more than enough to sustain a family through a long winter. But subsistence hunting of moose has become increasingly rare as the species faces numerous threats, like disease, that come with climate change. Moose are disappearing from northeast Minnesota, where it’s estimated they once numbered over 10,000. Since 2006, the population in the state has fallen by 64 percent.

“The moose is declining directly as a result of climate change,” said Seth Moore, a biologist who studies the animals and collaborates with McCormick’s tribe, the Grand Portage Band of Lake Superior Chippewa, on moose conservation.

When the Ojibwe first encountered European settlers in the early 1600s, their territory stretched some 2,000 miles, from Lake Ontario to the northern Great Plains in present-day Canada. In just a few hundred years, descendants of those settlers engineered an extractive economy based around commodity farming, mining, and oil and gas. Today, Ojibwe homelands are a fraction of what they once were, and the fossil fuel economy continues to raise global temperatures, changing the life cycles — and even the shapes and sizes — of species large and small.

Dwindling populations of species like the moose demonstrate how second- and third-order effects of climate change can upend ecosystems that have sustained human life, ancestral knowledge, and culture for generations. In southeast Alaska, for example, Indigenous peoples have documented a reduced harvest of Pacific salmon due to warmer waters. In the northern Great Lakes region, wild rice that Anishinaabe communities like McCormick’s have long depended on can’t properly take root during warming winters. (The Anishinaabe are a culturally related group of tribes that includes the Ojibwe.)

Minnesota’s moose are the same species found in, say, Maine or eastern Canada. (North America’s moose comprise four subspecies; notably, moose in Maine are facing many of the same threats.) But if moose in Minnesota’s boreal forests were to blink out, not only would the downstream ripples be felt across the web of life, the region’s original human inhabitants and environmental stewards would lose an important piece of their identity, too.

The moose plays a sacred role in Ojibwe culture

As long as the Ojibwe have been here, they have depended on and revered the moose. Yet that history has been erased from the popular consciousness. “If people would have taken the time to learn more about the Anishinaabe, what would this country look like?” asked Jeff Tibbetts, a member of the Fond du Lac Band of Lake Superior Chippewa who also harvests moose. “I think it would be a lot stronger.”

Tibbetts, McCormick, and other Indigenous people who consider the moose a non-human relative face an existential dilemma. “Most people know about the relationship between the Plains Indians and the buffalo,” said Carl Gawboy, an Ojibwe painter who lives near Duluth, Minnesota (and features moose in many of his works). But few understand that a similar tie exists between the Ojibwe and the moose, he adds.

Gawboy’s ancestors played games with small pieces made from moose antlers; they made rattles from the hooves, stockings from the hocks, and snowshoe lashings and other kinds of clothing from the hides, he explained. Some Indigenous artists continue to practice traditional moose hair embroidery, he said.

The moose is also core to the social fabric of many Ojibwe communities. “If someone does something for you,” McCormick explained, “a kind gesture would be to pull out a pound of moose meat to say thank you.”

After McCormick shot her first moose as a teenager, she knelt beside it and said a prayer of thanks. Later, she took the tongue — a delicacy — to an elder in the community. “This is something that has given its life so that I can live,” McCormick said, “so that my family can live.”

But a few years later, the moose started to vanish from those same woods.

A moose mystery was solved with GPS collars and helicopters

At first it was unclear what, exactly, was to blame.

In a healthy moose population, the adult mortality rate is typically between 8 and 10 percent, according to Moore. But starting about a decade ago, when McCormick’s tribe tapped Moore to help them figure out why moose were disappearing from northern Minnesota, the rate was closer to 20 percent.

Moore had seen aerial surveys showing how rapidly the massive herbivores were vanishing, but still, “at the beginning it was a total mystery,” Moore told Vox. “We had no idea what was causing it.”

Their focus initially turned to another iconic North American species: gray wolves. Over the past three decades, the region’s wolf population has grown exponentially. Warmer winters have made the northeastern woods hospitable to their primary food source — white-tailed deer. So when Moore and his team first began studying the moose decline here in 2010, they thought that wolf packs eating adult moose was likely a leading cause. And they were right that wolves were a factor — but it wasn’t adults they were killing.

“In the spring, moose calves are the easiest thing to eat,” Moore said. He and his team have since found that eight of every 10 moose calves born in northeast Minnesota are now killed by wolves in their first two weeks of life. Such a high calf mortality rate means adult moose aren’t being replenished when they die.

But the major killers of adult moose were altogether different. And it took a lot of intensive research to figure it out.

Several times each winter, Moore and his colleagues would go up in a helicopter to survey for moose. (The team does this work by air because the territory is so vast and unpopulated by people — plus, seeing a wild moose is a rare occurrence.) When they spotted one, they would dart the animal with a tranquilizer gun, bring the chopper down, and then hike to it.

Over the course of a decade, the researchers outfitted more than 160 adult moose with GPS collars to track their movements and activity level. If a moose stops moving for more than six hours, Moore gets a text alert with the animal’s location. “We’ll put together a team and head out, sometimes miles into the woods,” Moore said. “When we get there, typically, we’ll find a dead moose.”

Moore and his team then take blood and tissue samples from the moose’s body and send them to a lab, where technicians determine a cause of death.

After the researchers had accumulated three years’ worth of data, they started to see patterns that suggested that wolves, along with human recreational hunting, weren’t primary forces hurting the adult moose, after all.

The biggest threats were smaller creatures but just as dangerous.

Climate change means it’s boom times for brainworms and ticks

When Moore’s team began getting tissue sample results back after their first few winters collecting data, they pinned the leading cause of moose death in northeast Minnesota on a culprit that could fit in the palm of your hand: a type of parasitic brainworm.

An odd downstream effect of climate change is that these 2- to 3-inch long critters are catching rides in from elsewhere — and are overwhelming the moose. These freeloaders have slipped into this region via white-tailed deer, a host that the worms have co-evolved with and don’t cause any harm to (even though they burrow into the deer’s brains).

White-tailed deer and North American moose don’t normally share habitat; the deer’s shorter legs and thinner fur aren’t suited for the deep snow and subzero temperatures that moose prefer. But in the past few decades, as temperatures have risen and snow depths have shrunk, deer have been shifting northward into moose territory — and they’ve been taking the brainworms with them.

Brainworms eventually hatch into the deer’s bloodstream and then get dumped in their feces. On the forest floor, snails and slugs consume the deer droppings and then climb trees and shrubs, to be inadvertently eaten by foraging moose.

What happens next is dire. After the eggs hatch inside the moose’s brain, the worms tunnel around and, unlike in deer, cause serious neurological damage. Brainwormed moose show telltale signs of infestation — they walk in aimless circles, heads tilted to one side. They die either of starvation or hypothermia from loss of body fat.

Warmer winters are also driving the second-biggest moose killer that Moore and his team discovered: ticks.

Climate change has caused a tick explosion by melting away what has typically kept their numbers in check. Northern Minnesota’s ticks survive the cold winter by attaching themselves to the warm, thick coats of moose. In the spring, the ticks fall to the ground to lay eggs. Ice and snow used to kill a sizable portion of them before they could do so. But that crusty layer is melting earlier than ever, so now more ticks survive, resulting in skyrocketing populations. It’s enough for fatal tick infestations.

Moore and his colleagues have found moose covered in thousands of ticks. To relieve some of the pain and itching, moose will rub against trees, often wearing off patches of fur. Moose infested with ticks are typically missing 60 to 70 percent of their coat, according to Moore. Without their fur to protect them from the harsh winters, they often die from hypothermia or blood loss.

“It’s horrifying looking,” he said. “They’re called ‘ghost moose’ because their skin is much lighter than their hair.”

“It’s a never-ending battle”

Jeff Tibbetts still goes out moose hunting most seasons, but unlike in previous years, he often comes home empty-handed. There just aren’t as many moose out there, he says. He’s clear-eyed about what this could mean for his tribe — “if the numbers get too low,” he said, “we’ll stop hunting them.” But he does see evidence from Moore’s team, showing that the population has begun to stabilize in the last two years, as a reason for hope. (Moore said this could be due to recent severe winters, which dropped the number of brainworm-carrying deer in the region and also brought deeper snow, meaning more ticks are dying before they have a chance to attach to moose.)

Tibbetts’s tribe decides as a group how many hunting permits to give each season. Tibbetts also sees it as his and his tribe’s responsibility to maintain healthy moose habitat. That includes limiting carbon dioxide and other greenhouse gases, which is part of the reason why, he says, so many Indigenous people are on the front lines fighting against oil pipelines like the Dakota Access Pipeline and Enbridge Line 3.

Hundreds of years ago, the Ojibwe signed treaties that guaranteed their right to continue to hunt, fish, and gather wild foods on lands they ceded to the US government. If species like the moose can no longer thrive on those lands because of state and federal policies that promoted fossil fuel use, many Indigenous people see that as a violation of those treaties, and intend to fight to protect those rights.

“The resiliency of native people can’t be questioned,” Tibbetts said. “It’s a never-ending battle.”